1. Field of the Invention
The present invention relates to a method of treating synthetic fiber, and more particularly, to an improved method of giving a water absorption property and an antistatic property to synthetic fiber by treating the fiber with a water-soluble polymerizable monomer and its polymerization initiator. In the specification and claims, the term "synthetic fiber" means synthetic fiber and synthetic fiber fabric, and may be merely referred to as fiber.
2. Description of the Prior Art
A so-called graft polymerization modification method is known in which synthetic fiber is treated with a treating liquid containing a water-soluble polymerizable monomer, such as acrylic acid, acrylic acid amide or the like, and its polymerization initiator to give a water absorption property, an antistatic property and the like to the fiber. The inventors have already proposed in Japanese Patent Application Publication No. 30,640/76 a method of treating a synthetic fiber with a treating liquid containing an acrylamide derivative, such as N,N'-methylene-bis-acrylamide or the like, an acid and a polymerization initiator. According to that method, a durable antistatic property, water absorption property and hygroscopicity and an excellent feel can be given to synthetic fiber at the same time.
However, in those methods, since the one-bath immersion treating method, wherein synthetic fiber is treated in a bath containing both monomer and polymerization initiator, is generally used, a large amount of homopolymer is formed in the bath due to the self-polymerization of the monomer before a polymer film is formed on the fiber, and the homopolymer adheres to the fiber to deteriorate the feel of the fiber and to affect adversely the treating effect, and further the homopolymer contaminates the treating apparatus. Therefore, not only the cleaning of the treating apparatus is troublesome, but also the production of the treated fiber is expensive due to the loss of monomer. In a method wherein synthetic fiber is applied with the above described treating liquid containing both monomer and polymerization initiator by padding or spraying and then is heat treated, the treating liquid is not sufficiently stable, and homopolymer is formed in the treating liquid due to a slight rise of the temperature after the treating liquid is produced. Further, when the treating liquid contains acid, the polymerization initiator is decomposed due to the action of the acid and a small amount of metal ions contained in the water used, and the catalytic action of the polymerization initiator often lowers with the passing of time. Therefore, polymer is not uniformly formed on the fiber, the treating effect varies, and continuous production of treated fiber having uniform antistatic property and water absorption property is difficult.
Moreover, in the conventional methods, it is difficult for the monomer to penetrate into the interior of fiber and to form a polymer in the interior of the fiber. As a result, retention of the polymer in the fiber is reduced, and the treated fiber is always unsatisfactory in the durability of the antistatic property and water absorption property.